Mizar, Alcor and Jupiter

The city of Leiden houses the world’s oldest operating university-associated observatory. It was founded in 1633 and has been a renowned astronomical institute pretty much ever since. The modern astronomy department is located at the edge of the city, but closer to the centre, the so-called Old Observatory still stands. It houses a couple of antique telescopes, including one from 1838. All of them continue to be operational, although they are no longer used for real science. (Much more powerful telescopes are available at locations with much better weather and no urban light pollution.)

I attended an instruction class a couple of months ago to learn how to operate these telescopes, and I’ve used them a couple of times since. They are well suited for looking at objects like the moon, Jupiter, Saturn, various double stars and, with clear conditions, fainter stuff such as the Orion Nebula or the Andromeda Galaxy. Yesterday I was there again to help out with a tour of the Old Observatory for a group of optical mechanics.

I pointed the 1945 45-cm (18-in) telescope at two objects that always do well with these tours. The first one was the rather famous double star in the Big Dipper, called Mizar and Alcor. With good eyesight and under good conditions, one doesn’t need a telescope to distinguish the two stars, but the telescope does make it much easier. Furthermore, Mizar (the brighter of the two) turns out to be a double star itself. With even more advanced equipment, both components are in turn found to be double stars as well. So, we have two stars (revolving around each other) revolving around two other stars (also revolving around each other), together revolving around a single star, for a total of five stars.

When everyone was done looking at this, I moved the telescope over to Jupiter, the largest planet in our solar system, and one of the brightest objects in the night sky. Some of the characteristic atmospheric bands were visible, as were five of Jupiter’s moons. Up to now I’d never seen more than four, so that was a nice surprise.

The group had to get back to their bus at that point, so we couldn’t watch anything else. Still, everyone seemed to be really excited, which always helps for me to also enjoy myself.